Tris(boratabenzene) Lanthanum Complexes: Synthesis, Structure, and Reactivity

A series of tris­(boratabenzene) lanthanum
complexes were synthesized
and structurally characterized. Salt elimination of anhydrous LaCl3 with Li­[C5H5BR] (R = H, NEt2) provided tris­(boratabenzene) lanthanum complexes [C5H5BH]3­LaLiCl (1) and [C5H5BNEt2]3­LaLiCl­(THF)
(2) in high yields. Hydroboration of 1-hexene or 3-hexyne
with 1 gave the alkyl- or alkenyl-functionalized boratabenzene
lanthanum complexes, [C5H5B­(CH2)5CH3]3­LaLiCl­(THF) (3) and [C5H5BC­(C2H5)CH­(C2H5)]3­LaLiCl­(THF) (4), in good yields. Hydroboration of N,N′-diisopropylcarbodiimide with 1 gave the monohydroboration
product [C5H5BN­(iPr)­CHN­(iPr)]­[C5H5BH]2La (5) due to the steric
bulk of the [C5H5BN­(iPr)­CHN­(iPr)]− ligand. Complex 5 can undergo further hydroboration
with 3-hexyne or dehydrogenative coupling with phenyl acetylene to
afford [C5H5BN­(iPr)­CHN­(iPr)]­[C5H5BC­(C2H5)CH­(C2H5)]2La (6) or [C5H5BN­(iPr)­CHN­(iPr)]­[C5H5BCCPh)]2La (7).